WinForm实现无边框窗体的拖动

一个登录窗体，FormBorderStyle属性设置为None,打开后不能挪动位置，有时候会妨碍使用，有点恶心。网上找了段内容，实现拖动效果：

        #region 无边框拖动效果,Form被PictureBox覆盖，Form事件不会被触发

        [System.Runtime.InteropServices.DllImport("user32.dll")]
        public static extern bool ReleaseCapture();
        [System.Runtime.InteropServices.DllImport("user32.dll")]
        public static extern bool SendMessage(IntPtr hwnd, int wMsg, int wParam, int lParam);
        [System.Runtime.InteropServices.DllImportAttribute("user32.dll")]
        internal static extern int SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);

        public const int WM_SYSCOMMAND = 0x0112;
        public const int SC_MOVE = 0xF010;
        public const int HTCAPTION = 0x0002;
        private void pictureBoxBackground_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                ReleaseCapture();
                SendMessage(this.Handle, WM_SYSCOMMAND, SC_MOVE + HTCAPTION, 0);
            }
        }

        public const int WM_NCLBUTTONDOWN = 0xA1;
        public const int HT_CAPTION = 0x2;
        public const int MOUSEWHEEL = 0x020A;
        private void pictureBoxBackground_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                ReleaseCapture();
                SendMessage(Handle, WM_NCLBUTTONDOWN, HT_CAPTION, 0);
            }
        }
        #endregion